1. Field of the Invention
The present invention relates to a sheet detecting apparatus and more specifically to an apparatus for detecting an object in the form of a sheet moving past a flat conveying path.
2. Discussion of Related Art
In a known apparatus described in European Patent Application EP-A-0058285 a beam of light emitted by a light-emitting element is deflected by the first light-reflecting surface of a light-reflecting element and projected directly on to the second light-reflecting surface, which second light-reflecting surface deflects the beam of light incident thereon towards a light-sensitive element. This known apparatus is very sensitive to changes in the position of the light-reflecting element with respect to the light-emitting element and the light-sensitive element in a direction parallel to the conveying path for the sheet form object. In the known apparatus, in the event of such a change of position by the light-reflecting element, the distance between the beam of light projected on to the first light-reflecting surface and the beam of light reflected by the second light-reflecting surface changes by an amount which, given parallelism of the beams of light, is equivalent to twice the distance over which the light-reflecting element is displaced in the path direction. The result is a risk that the beam of light will fall completely or partially beside the light-sensitive element, so that even in the absence of an object in the form of a sheet interrupting the beam of light, the light sensitive element will react as if an object in the form of a sheet were present.